The invention relates to a filtration apparatus with exchangeable filters for the filtration of fluids contaminated with solid particles. The apparatus comprising a tubular filter housing of fluid-impermeable material, provided with an extending central bore, intended for the receiving therein of filter cartridges that can be slided in and out of the bare. The filter housing has a fluid entrance opening and a fluid exit opening, which have been provided in the tube walls of the filter housing in relative displacement to each other, and interchangeable filter cartridges, each one consisting of a hollow, tubular filter element that encloses a filter chamber, closed at the front and rear ends by end caps of fluid-impermeable material, of which the outer circumferences have been adapted to the size of the central bore in the filter housing, and with the one end cap having an opening in communication with the filter chamber of the filter element, which, with proper positioning of the filter cartridge in the central bore of the filter housing, provides an open connection with the one of the entrance and exit openings of the filter housing, while the other one provides an open connection with the outer wall of the filter element, and with seals between the end caps and the inner wall of the central bore ensuring that the fluid communication between the entrance and exit openings is only through the filter.
Such a filtration apparatus is known from the U.S. Pat. No. 3,984,325 to Rosaen. A cylindrical, tubular filter housing is used in this known apparatus, of which the central bore is capable of receiving several, at least two, filter cartridges. The fluid entrance and exit openings have been provided approximately in the centre of the filter housing. Each filter cartridge has a rear end cap that is provided with a central screw bore. The front end cap, which seals the filter cartridge, has a narrowed screw piece at its front end, which is intended to be screwed on to the rear end cap of a filter cartridge lying in front of it. This screw piece is hollow, with this cavity having a side-wise extension towards the outside at the rear side. In case two such filter cartridges screwed together are within the cylindrical, tubular filter housing, then there is an annular cavity, which is in connection with the internal space of the filter element, between the rear end cap of the filter element at the front and the front end cap of the filter element at the rear. This annular cavity forms an annular channel together with the inner wall of the central bore, which, with a proper positioning of the filter cartridges, lies just in front of the one of the entrance and exit openings, while the other one of these openings is in communication with the outer wall of the filter element, so that fluid communication between the entrance and exit openings through the filter is possible.
Each filter cartridge is further provided with seals in the form of O-shaped rings in each of the end caps of a filter cartridge.
With this filter apparatus it is possible to continue fluid filtration without interruption, even when a soiled filter is to be exchanged. During operation there are always two filter cartridges in the filter housing, of which the front one is used and the rear one is on stand-by. When the filter at the front is contaminated to the extent that it must be exchanged, then a new filter cartridge is introduced at the rear end of the filter housing, and screwed onto the the rear of the filter cartridges present in the housing, and subsequently pushed through, by which the contaminated filter is pushed forwards, and can be screwed loose and removed, while the filter cartridge lying just behind has now taken over the filtration function.
Although this known filtration apparatus has the advantage that a new, clean filter cartridge can be introduced during operation, it exhibits a number of disadvantages. For example, it is not suitable for applications in which coarse pollutants must be filtered from a fluid, such as with filtrations during applications in hospitals, dentists' clinics, and such. A dental application often involves rinsing water, which, for example, contains amalgam grindings, and in case the fluid is let in through opening 14 of the Rosaen filter device, these amalgam grindings, both fine and coarse, will rapidly clog the space 46 between this entrance opening and the filter element 28 during use. In the opposite case, in case the entrance of fluid of the rinsing water occurs through opening 16, the annular space 54 shall clog rapidly, so that the filter element proper cannot be used effectively.
Another disadvantage is that during the exchange of a filter a new filter to be introduced must be screwed on with a probability that this screwing on does not occur properly, while the soiled filter cartridge coming out must be screwed loose, which implies that the soiled filter must be held by hand, and when this screwing off takes place with some force, there moreover is a probability that an operation glove is damaged, and that, for example, in the case of a filtrate of blood and saliva, infection can occur.